Dermoscopy is the term used to describe methods of imaging skin lesions. Skin is the largest organ in the body and it is the most easily accessible organ for external optical imaging. For early detection of cancers, it is important that the skin be medically examined for lesions.
With over forty (40%) percent of the cancers occurring on the skin (American Cancer Society Statistics 2001, Perelman 1995), and incidence of skin cancer increasing each year, tools and methods of imaging skin lesions are becoming increasingly important. Most of the cancers detected on the skin are Basal Cell Carcinoma (BCC) and Squamous Cell Carcinoma (SSC), which are differentiated from melanoma, a more deadly form of skin cancer. The early detection of skin cancer allows for inexpensive treatment before the cancer causes more severe medical conditions. Thus, there is a great need in the art for simple inexpensive instruments that allow for the early screening for skin cancer.
Because skin is partially translucent, dermoscopy utilizes tools for visualization of the pigmentation of the skin below the surface. In this regard, when attempting to visualize the deeper structure of the skin, it is important to reduce the reflection of light from the skin which may obscure the underlying structures. Methods used to reduce the surface reflection from the skin are referred to as epiluminescence imaging. There are three known methods for epiluminescence imaging of the skin, oil-immersion, cross-polarization, and side-transillumination. Oil-immersion and cross-polarization methods have been extensively validated for early skin cancer detection while side transillumination methods are currently undergoing study and clinical validation.
Oil-immersion devices are generally referred to as Dermatoscopes. Dermatoscopes permit increased visualization of sub surface pigmentation by using a magnification device in association with a light source. In operation, oil is placed between the skin and a glass faceplate. The placement of oil and a glass interface between the eye and the surface of the skin reduces the reflected light from the skin, resulting in deeper visualization of the underlying skin structure.
While oil-immersion has proved to be an excellent method of epiluminescence imaging of the skin, demonstrating improved sensitivity for melanoma detection, it is messy and time consuming for the physician. As a result, the Dermatoscope is used mostly by physicians that specialize in pigmented lesions and for evaluation of suspicious lesions that cannot be diagnosed visually. Also, the oil-immersion of the Dermatoscope has been found to be less effective for BCC and SCC imaging. The pressure created by the compression of the glass faceplate causes blanching of blood vessels in the skin resulting in reduced capability of the Dermatoscope for imaging the telangiectesia that is often associated with BCC or other malignent lesions.
Cross-polarization or orthogonal polarization is another method of reducing the reflection of the light from the surface of the skin to aid in the medical examination of the skin. Light emanating from a light source is first linearly polarized, so that the orientation of the light falling on the skin surface is in the same plane of polarization. As the light enters the skin, its polarization angle changes such that the light is reflected from a deeper structure. However, the light reflected from the surface of the skin is still polarized in the same plane as the incident light. By including a second polarizer in the path of the reflected light from the skin, a selective filtering of light can be achieved.
Most of the light directed to the skin's surface is reflected as the refractive index of skin is higher than that of air. The reflection of light, off of the skin, is analogous to the reflection of light off of the surface of water. Accordingly, the information received by the eye carries mostly information about the contour of the skin surface rather than the deeper structures. Remaining light enters the skin and is absorbed or is reflected back in a scattered fashion. By polarizing the incident light with a second of polarizer, the specular component of the reflected light is blocked by the viewing polarizer, thus producing an enhanced view below the skin surface. Accordingly, inflammation, color, pigmentation, hair follicles and blood vessels may be viewed.
When the incident light and the second polarizer are parallel, the surface topography and properties of the skin are highlighted and enhanced. In this regard, if the polarizer in the path of the light from the skin to the eye is polarized in the same orientation of the incident light, only the light from its polarization angle will be allowed to pass through the lens. Cross-polarization imaging of the body was originally described by R. R. Anderson (“Polarized light examination and photography of the skin.” Archives Dermatology 1991; 127; 1000–1005). Later, Binder introduced the MoleMax manufactured by Derma Instruments (Vienna, Austria) for the examination and mapping of pigmented lesions. Binder further developed the no-oil cross-polarization epiluminescence method. MoleMax, however, while validating clinically the improved diagnosis and accuracy without the use of oil, still used a glass faceplate and video imaging system to execute skin examinations.
In light of many of the difficulties associated with prior dermoscopy systems, a simple and cost-effective diagnostic systems remained unavailable for general dermatologists to use on a routine clinical basis. Dermoscopy, until recently, remained generally a research tool utilized in special clinical cases.
More recently, however, a substantial advancement in skin cancer detection occurred through a simple device identified as DermLite®, manufactured and marketed by 3Gen, LLC. of Monarch Beach, Calif. With this low cost and easy to use DermLite® Device, screening for cancer by dermatologists in routine clinical examination of skin disease has become a reality. The DermLite® device uses cross-polarization epiluminescence imaging through use of white light emitting diodes (LEDs), a high magnification lens (10×), and a lithium ion battery contained in a small lightweight device.
In the DermLite® device, a window is incorporated into a compact housing, and a plurality of white light LEDs encircle a magnifying lens. The DermLite® device incorporates cross-polarization filters that reduce the reflection of light from the surface of the skin and permits visualization of the deeper skin structures. Light from eight (8) LEDs is polarized linearly by a polarizer, which is annular in shape and located in front of the LEDs. The imaging viewed through the magnifying lens is also linearly polarized by using a polarizer that is located in front of the lens. The LEDs have a narrow beam angle that concentrates the light into a small area, pointing the incident light to the center to increase the brightness of the area being viewed. Thus, light from the LEDs passes through the polarizer which enters the skin and reflects back through the viewing polarizer to create cross-polarization allowing examination to look deeper within the skin structure. Although, the DermLite® product has been recognized as a major advancement in the art of routing clinical diagnosis and analysis of skin cancer lesions, DermLite® device does not provide a mechanism for enabling the user to additionally view parallel-polarized light, or a combination of cross-polarized light and parallel-polarized light.
The DermLite® Platinum® product, also manufactured by 3Gen, LLC. was developed to provide variable polarization. Variable polarization is achieved by a rotating dial. Rotation of the polarizer to a cross-polarization cancels out the surface reflection for an in-depth look at the deeper pigmentation in lesion structure. Rotation to parallel polarization allows a clear view of the skin surface. The DermLite® Platinum® product requires manual manipulation of the dial which may cause user to lose the viewing spot, or otherwise interfere with examination. Further, DermLite Platinum® does not provide a user the ability to view the skin with an instantaneous switch over from cross-polarization to parallel polarization.
Recent discoveries in optical fluorescence imaging have identified several molecules having fluorescence properties that are useful in medicine. In dermatology, simple applications such as delta-aminolaevulinic acid (ALA) applied topically have been found to enhance the visualization of basal cell cancer from normal tissue, when illuminated with UV/Blue light. Fluorescein is another fluorescent compound that has been in clinical use in opthamology for several years and has great potential for use in dermatological applications. Indocyanine green (ICG), Methylene Blue, and ethyl nile blue are contrast agents that are used to increase light absorption in blood vessels. There are several FDA approved optical fluorescence tracers already approved for clinical use, and several more new probes may be applicable in the future. However, the use of fluorescence imaging of the skin has been illusive for clinical dermatologist because of the complexity and costs of the associated equipment.
In current applications, such as in the application of ALA topically to a basal cell carcinoma to a BCC, conventional white light visual images of the BCC are displayed next to the fluorescence excited images of ALA in the BCC. The ALA is taken up by the active areas of cancer, converted to porphyrin IX, and fluoresces when exposed to UV/Blue light. It becomes apparent that the fluorescent areas of the BCC may not coincide with the anatomical features of the BCC as shown in white light. Currently the side-by-side comparison is only available by taking two separate images and co-registering these images later in the computer.
Thus, there is a great need in the art for a device that will allow clinical viewing of skin lesions which provides on demand switching from cross-polarized imaging to parallel-polarized imaging and a combination of both. Further there is a great need in the art for a clinical viewing of skin lesions that can toggle back and forth from a white light to a colored or UV light in order to contrast and compare images.